How to soft wash tarmac, including driveways and car parks?

March 01, 2024

Soft washing tarmac driveway with Benz Bio Cleanze DDAC softwash biocide

Tarmac attracts algae, moss, mould and lichen – which needs to be periodically cleaned by soft washing.

In our experience the most effective soft wash product for treating tarmac is usually Benz Bio Cleanze.

Tarmac can be treated directly with Bio Cleanze, although carefully pre-scraping or pressure washing heavy moss prior to treatment will ensure the maximum effectiveness of Bio Cleanze.

If, when scraping the moss there is still a level of growth which cannot be removed, then brushing-in the application of Bio Cleanze is useful to ensure the whole surface has been treated.

If the moss is below the top of the tarmac, spraying alone will often suffice (the photo below shows an example where spraying, without pre-scraping, would be sufficient)

biocide treatment of tarmac softwashing

Moss will turn brown and wash out of the tarmac over the next few weeks and months through the natural action of sun, wind and rain. The start of this process can be seen in the photo below:

treating moss tarmac softwashing biocide benz


Quick tip: A follow up application at around 6 months, to deal with any remaining spores, is usually advisable.



What dilution of Bio Cleanze to use?

Apply at 25-50:1. Then follow up with regular "Clean & Maintain" treatments at 50:1 (40:1 in cold weather) every 12-24 months (depending on the local environment and other variable factors).

When treating tarmac with Bio Cleanze, the dilution for a specific job can vary from 25-50:1.

Quick tip: Although it is non-porous, because of its honeycomb-like structure tarmac can quite "thirsty". This means that giving a soft wash treatment can be more expensive than when treating a smoother surface such as concrete.

The actual dilution used depends on:

a) The external temperature. The colder it is the longer Bio Cleanze will take to work, which can be offset by using a stronger dilution.

b) The amount of moss or other biological growth.

c) How long moss has been allowed to grow into the tarmac.

d) Important: If children or animals will use the tarmac, apply Bio Cleanze at a maximum dilution of 50:1 and keep them away from the surface until it is completely dry.

e) If you can be 100% sure that no children or animals will be in contact with the surface, and you can ensure zero pooling of Bio Cleanze, then you can treat as strong as 20:1.

f) You can treat tarmac with Bio Cleanze whilst the surface is still wet immediately after power washing. But ensure all water pooling is brushed away first.


More quick tips:
1) We've found that a repeat application after 6 months, even if the tarmac looks clean, will considerably increase the longevity of the treatment – up to a couple of years in our experience.

The idea of the second treatment, even if the tarmac doesn't look as if it needs it, is to deal with any remaining spores that may still be present after the initial treatment.

2) Tarmac is a non-porous surface, which means that Bio Cleanze cannot offer the full residual protection against re-colonisation that it does on porous surfaces. But most growths will fade within 24-48 hours. Then nature will continue to cleanse the surface over time through the effects of sun, wind and rain.

3) Contact your customer at the 12-18 month mark to offer them a quick re-treatment. This will give you a steady stream of repeat business.

The selling point for regular soft washing treatments with Bio Cleanze is that your customer will enjoy a tarmac surface that is permanently clean. This is a similar principle to regularly cleaning windows so they are always clean, rather than waiting until they are filthy, which most people really appreciate.

Click here to learn about the Benz "Clean & Maintain" softwash systems


Can you use Benz Lightning Cleanze to soft wash tarmac?

Yes, Lightning Cleanze will kill the growths very quickly. Lightning Cleanze is the soft washing product of choice when your customer wants immediate results and does not want to wait for Bio Cleanze to work.

If your customer just wants a quick clean before putting their property on the market, for example, Lightning Cleanze may be the most effective choice of soft washing product.

The downside is that the biological growths on the tarmac can turn into a white mush that many customers don't like.

Fortunately, giving a light power wash will usually clear the mush.

Important: Be careful not to wash the rinse water into flower beds, lawns or surface drains (use only foul water drains and if these are not available suck up the rinse water and remove it from the site for safe dispoal). You will of course need to factor in the extra cost of power washing and collecting the mush into your quote.

Will tarmac be discoloured by soft washing?

Bio Cleanze will clean the tarmac giving the appearance of lightening the tarmac.

In our experience, Bio Cleanze leaves the tarmac pretty much in it's original colour. So when the surface is cleaned from whatever colonisation was present, it looks lighter than areas that have not been cleaned but the actual colour is unlikely to have changed much, if at all.

Lightning Cleanze however, will impart an actual lightening effect to the tarmac. This is why we suggest applying it at 10:1 dilution and whenever possible treating tarmac with Bio Cleanze as your first choice.

Quick tip: If Lightning Cleanze is applied at a dilution stronger than 10:1 the tarmac is much more likely to turn a light grey colour.

Some customers like this change of colour. Others do not. So always treat a small test patch at first and get your customer's agreement that they are happy with the results and give their agreement for you to clean the rest of the tarmac.

Our experience is that using Lightning Cleanze at 10:1 is the optimum choice for soft washing tarmac if your customer does not want to wait for the results of Bio Cleanze to show.

Quick tips:

    1. When using either product it's a good idea to treat the whole area of tarmac, which will impart a more universal colouring to the entire surface.
    2. Whichever product you choose to use, remove any heavy build up of moss and lichen by lightly scraping the tarmac prior to giving a softwash treatment. This can be very quick and reduces the quantity of softwash product you'll need to complete the job.
    3. Use either Bio Cleanze or Lightning Cleanze. There is nothing to be gained from soft washing a non-porous surface such as tarmac with both softwash products.

Click here to get more practical how-to tips for soft washing tarmac 

Quick tip: 
Enter a relevant "keyword" or short phrase into our in-site Search Engine to find answers to most of your softwashing questions (e.g. keyword for above link = "tarmac drive")

We hope this information is helpful and wish you great success in your soft washing business,

Benz Team

Order Benz softwash chemicals & equipment online or by phone:

GB (England, Scotland, Wales)

Phone: 0800 70 74 222 


Ireland and other countries

Phone: 00353 214 622 978


Lines open Monday - Friday, 9am – 5pm

Please note: The above phone numbers are for orders only (click here for tech support)

Click here to explore the extensive range of Benz softwash cleaning chemicals & equipment

Benz Softwash Bio Cleanze DDAC biocide & Benz Softwash Lightning Cleanze SH sodium hypochlorite biocide

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